If Hitler had mustered up just enough wisdom to realize that an invasion of the USSR would be disastrous and managed to contain his hatred of communism just enough to restrain himself from operation Barbarossa, he could likely have held most of Europe and a DDay type landing would have been unlikely to succeed. Nothing short of a nuclear bombardment of Europe would have dislodged them. One of the weirdest darkest historical hypotheticals. It’s amazing how much of history hinges on the personal flaws of specific leaders.